Printhead with double omega-shaped heater elements

ABSTRACT

An ink jet printhead has a plurality of nozzles and a bubble forming chamber corresponding to each of the nozzles respectively. The bubble forming chambers are adapted to contain a bubble forming liquid and a heater element is disposed in each of the bubble forming chambers respectively. The heater elements are configured for thermal contact with the bubble forming liquid and, a pair of electrodes for each of the heater elements are positioned adjacent each other such that the heater element provides a single current path between the electrodes of each pair. Each of the heater elements has a double omega shape in which a smaller, inner omega shape is concentric with, and encircled by, a larger, outer omega shape.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.11/926,121 filed on Oct. 28, 2007, now issued as U.S. Pat. No. 7,717,543which is a continuation of U.S. application Ser. No. 10/728,790 filedDec. 8, 2003, now issued as U.S. Pat. No. 7,287,836, which is acontinuation in part of U.S. application Ser. No. 10/160,273 filed onJun. 4, 2002, now issued as U.S. Pat. No. 6,746,105, which is acontinuation of U.S. application Ser. No. 09/112,767 filed on Jul. 10,1998, now issued as U.S. Pat. No. 6,416,167, all of which are hereinincorporated by reference.

The following Australian provisional patent applications are herebyincorporated by cross-reference. For the purposes of location andidentification, US patent applications identified by their US patentapplication serial numbers (USSN) are listed alongside the Australianapplications from which the US patent applications claim the right ofpriority.

US PATENT/PATENT CROSS-REFERENCED APPLICATION AUSTRALIAN (CLAIMING RIGHTPROVISIONAL OF PRIORITY FROM PATENT AUSTRALIAN PROVISIONAL DOCKETAPPLICATION NO. APPLICATION) NO. PO7991 6,750,901 ART01US PO85056,476,863 ART02US PO7988 6,788,336 ART03US PO9395 6,322,181 ART04USPO8017 6,597,817 ART06US PO8014 6,227,648 ART07US PO8025 6,727,948ART08US PO8032 6,690,419 ART09US PO7999 6,727,951 ART10US PO80306,196,541 ART13US PO7997 6,195,150 ART15US PO7979 6,362,868 ART16USPO7978 6,831,681 ART18US PO7982 6,431,669 ART19US PO7989 6,362,869ART20US PO8019 6,472,052 ART21US PO7980 6,356,715 ART22US PO80186,894,694 ART24US PO7938 6,636,216 ART25US PO8016 6,366,693 ART26USPO8024 6,329,990 ART27US PO7939 6,459,495 ART29US PO8501 6,137,500ART30US PO8500 6,690,416 ART31US PO7987 7,050,143 ART32US PO80226,398,328 ART33US PO8497 7,110,024 ART34US PO8020 6,431,704 ART38USPO8504 6,879,341 ART42US PO8000 6,415,054 ART43US PO7934 6,665,454ART45US PO7990 6,542,645 ART46US PO8499 6,486,886 ART47US PO85026,381,361 ART48US PO7981 6,317,192 ART50US PO7986 6,850,274 ART51USPO8026 6,646,757 ART53US PO8028 6,624,848 ART56US PO9394 6,357,135ART57US PO9397 6,271,931 ART59US PO9398 6,353,772 ART60US PO93996,106,147 ART61US PO9400 6,665,008 ART62US PO9401 6,304,291 ART63USPO9403 6,305,770 ART65US PO9405 6,289,262 ART66US PP0959 6,315,200ART68US PP1397 6,217,165 ART69US PP2370 6,786,420 DOT01US PO80036,350,023 Fluid01US PO8005 6,318,849 Fluid02US PO8066 6,227,652 IJ01USPO8072 6,213,588 IJ02US PO8040 6,213,589 IJ03US PO8071 6,231,163 IJ04USPO8047 6,247,795 IJ05US PO8035 6,394,581 IJ06US PO8044 6,244,691 IJ07USPO8063 6,257,704 IJ08US PO8057 6,416,168 IJ09US PO8056 6,220,694 IJ10USPO8069 6,257,705 IJ11US PO8049 6,247,794 IJ12US PO8036 6,234,610 IJ13USPO8048 6,247,793 IJ14US PO8070 6,264,306 IJ15US PO8067 6,241,342 IJ16USPO8001 6,247,792 IJ17US PO8038 6,264,307 IJ18US PO8033 6,254,220 IJ19USPO8002 6,234,611 IJ20US PO8068 6,302,528 IJ21US PO8062 6,283,582 IJ22USPO8034 6,239,821 IJ23US PO8039 6,338,547 IJ24US PO8041 6,247,796 IJ25USPO8004 6,557,977 IJ26US PO8037 6,390,603 IJ27US PO8043 6,362,843 IJ28USPO8042 6,293,653 IJ29US PO8064 6,312,107 IJ30US PO9389 6,227,653 IJ31USPO9391 6,234,609 IJ32US PP0888 6,238,040 IJ33US PP0891 6,188,415 IJ34USPP0890 6,227,654 IJ35US PP0873 6,209,989 IJ36US PP0993 6,247,791 IJ37USPP0890 6,336,710 IJ38US PP1398 6,217,153 IJ39US PP2592 6,416,167 IJ40USPP2593 6,243,113 IJ41US PP3991 6,283,581 IJ42US PP3987 6,247,790 IJ43USPP3985 6,260,953 IJ44US PP3983 6,267,469 IJ45US PO7935 6,224,780 IJM01USPO7936 6,235,212 IJM02US PO7937 6,280,643 IJM03US PO8061 6,284,147IJM04US PO8054 6,214,244 IJM05US PO8065 6,071,750 IJM06US PO80556,267,905 IJM07US PO8053 6,251,298 IJM08US PO8078 6,258,285 IJM09USPO7933 6,225,138 IJM10US PO7950 6,241,904 IJM11US PO7949 6,299,786IJM12US PO8060 6,866,789 IJM13US PO8059 6,231,773 IJM14US PO80736,190,931 IJM15US PO8076 6,248,249 IJM16US PO8075 6,290,862 IJM17USPO8079 6,241,906 IJM18US PO8050 6,565,762 IJM19US PO8052 6,241,905IJM20US PO7948 6,451,216 IJM21US PO7951 6,231,772 IJM22US PO80746,274,056 IJM23US PO7941 6,290,861 IJM24US PO8077 6,248,248 IJM25USPO8058 6,306,671 IJM26US PO8051 6,331,258 IJM27US PO8045 6,110,754IJM28US PO7952 6,294,101 IJM29US PO8046 6,416,679 IJM30US PO93906,264,849 IJM31US PO9392 6,254,793 IJM32US PP0889 6,235,211 IJM35USPP0887 6,491,833 IJM36US PP0882 6,264,850 IJM37US PP0874 6,258,284IJM38US PP1396 6,312,615 IJM39US PP3989 6,228,668 IJM40US PP25916,180,427 IJM41US PP3990 6,171,875 IJM42US PP3986 6,267,904 IJM43USPP3984 6,245,247 IJM44US PP3982 6,315,914 IJM45US PP0895 6,231,148IR01US PP0869 6,293,658 IR04US PP0887 6,614,560 IR05US PP0885 6,238,033IR06US PP0884 6,312,070 IR10US PP0886 6,238,111 IR12US PP0877 6,378,970IR16US PP0878 6,196,739 IR17US PP0883 6,270,182 IR19US PP0880 6,152,619IR20US PO8006 6,087,638 MEMS02US PO8007 6,340,222 MEMS03US PO80106,041,600 MEMS05US PO8011 6,299,300 MEMS06US PO7947 6,067,797 MEMS07USPO7944 6,286,935 MEMS09US PO7946 6,044,646 MEMS10US PP0894 6,382,769MEMS13US

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to the field of inkjet printers and,discloses an inkjet printing system using printheads manufactured withmicroelectro-mechanical systems (MEMS) techniques.

BACKGROUND OF THE INVENTION

Many different types of printing have been invented, a large number ofwhich are presently in use. The known forms of print have a variety ofmethods for marking the print media with a relevant marking media.Commonly used forms of printing include offset printing, laser printingand copying devices, dot matrix type impact printers, thermal paperprinters, film recorders, thermal wax printers, dye sublimation printersand ink jet printers both of the drop on demand and continuous flowtype. Each type of printer has its own advantages and problems whenconsidering cost, speed, quality, reliability, simplicity ofconstruction and operation etc.

In recent years, the field of ink jet printing, wherein each individualpixel of ink is derived from one or more ink nozzles has becomeincreasingly popular primarily due to its inexpensive and versatilenature.

Many different techniques on ink jet printing have been invented. For asurvey of the field, reference is made to an article by J Moore,“Non-Impact Printing: Introduction and Historical Perspective”, OutputHard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

Ink Jet printers themselves come in many different types. Theutilization of a continuous stream of ink in ink jet printing appears todate back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hanselldiscloses a simple form of continuous stream electro-static ink jetprinting.

U.S. Pat. No. 3,596,275 by Sweet also discloses a process of acontinuous ink jet printing including the step wherein the ink jetstream is modulated by a high frequency electro-static field so as tocause drop separation. This technique is still utilized by severalmanufacturers including Elmjet and Scitex (see also U.S. Pat. No.3,373,437 by Sweet et al)

Piezoelectric ink jet printers are also one form of commonly utilizedink jet printing device. Piezoelectric systems are disclosed by Kyseret. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragmmode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) whichdiscloses a squeeze mode of operation of a piezoelectric crystal, Stemmein U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectricoperation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectricpush mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No.4,584,590 which discloses a shear mode type of piezoelectric transducerelement.

Recently, thermal ink jet printing has become an extremely popular formof ink jet printing. The ink jet printing techniques include thosedisclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S.Pat. No. 4,490,728. Both the aforementioned references disclosed ink jetprinting techniques that rely upon the activation of an electrothermalactuator which results in the creation of a bubble in a constrictedspace, such as a nozzle, which thereby causes the ejection of ink froman aperture connected to the confined space onto a relevant print media.Printing devices utilizing the electro-thermal actuator are manufacturedby manufacturers such as Canon and Hewlett Packard.

As can be seen from the foregoing, many different types of printingtechnologies are available. Ideally, a printing technology should have anumber of desirable attributes. These include inexpensive constructionand operation, high speed operation, safe and continuous long termoperation etc. Each technology may have its own advantages anddisadvantages in the areas of cost, speed, quality, reliability, powerusage, simplicity of construction operation, durability and consumables.

In the construction of any inkjet printing system, there are aconsiderable number of important factors which must be traded offagainst one another especially as large scale printheads areconstructed, especially those of a pagewidth type. A number of thesefactors are outlined in the following paragraphs.

Firstly, inkjet printheads are normally constructed utilizingmicro-electromechanical systems (MEMS) techniques. As such, they tend torely upon standard integrated circuit construction/fabricationtechniques of depositing planar layers on a silicon wafer and etchingcertain portions of the planar layers. Within silicon circuitfabrication technology, certain techniques are better known than others.For example, the techniques associated with the creation of CMOScircuits are likely to be more readily used than those associated withthe creation of exotic circuits including ferroelectrics, luminiarsenide etc. Hence, it is desirable, in any MEMS constructions, toutilize well proven semi-conductor fabrication techniques which do notrequire any “exotic” processes or materials. Of course, a certain degreeof trade off will be undertaken in that if the advantages of using theexotic material far out weighs its disadvantages then it may becomedesirable to utilize the material anyway. However, if it is possible toachieve the same, or similar, properties using more common materials,the problems of exotic materials can be avoided.

With a large array of ink ejection nozzles, it is desirable to providefor a highly automated form of manufacturing which results in aninexpensive production of multiple printhead devices.

Preferably, the device constructed utilizes a low amount of energy inthe ejection of ink. The utilization of a low amount of energy isparticularly important when a large pagewidth full color printhead isconstructed having a large array of individual print ejection mechanismwith each ejection mechanisms, in the worst case, being fired in a rapidsequence.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an ink ejectionnozzle arrangement suitable for incorporation into an inkjet printheadarrangement for the ejection of ink on demand from a nozzle chamber inan efficient and reliable manner.

According to a first aspect, the present invention provides an ink jetprinthead comprising:

a plurality of nozzles;

a bubble forming chamber corresponding to each of the nozzlesrespectively, the bubble forming chambers adapted to contain a bubbleforming liquid; and,

at least one heater element disposed in each of the bubble formingchambers respectively, the heater elements configured for thermalcontact with the bubble forming liquid; such that,

heating the heater element to a temperature above the boiling point ofthe bubble forming liquid forms a gas bubble that causes the ejection ofa drop of an ejectable liquid through the nozzle corresponding to thatheater element; wherein,

the bubble forming chamber has a circular cross section.

By designing the bubble forming chamber with a circular cross section,it has much greater structural strength and rigidity. The circulargeometry avoids areas of high stress concentration that are prone tofailure. The use of an inherently high strength structure allows it touse less material and have a more compact design which improves thenozzle density of the printhead. This in turn improves the printingresolution.

According to a second aspect, the present invention provides a printersystem which incorporates a printhead, the printhead comprising:

a plurality of nozzles;

a bubble forming chamber corresponding to each of the nozzlesrespectively, the bubble forming chambers adapted to contain a bubbleforming liquid; and,

at least one heater element disposed in each of the bubble formingchambers respectively, the heater elements configured for thermalcontact with the bubble forming liquid; such that,

heating the heater element to a temperature above the boiling point ofthe bubble forming liquid forms a gas bubble that causes the ejection ofa drop of an ejectable liquid through the nozzle corresponding to thatheater element; wherein,

the bubble forming chamber has a circular cross section.

According to a third aspect, the present invention provides a method ofejecting drops of an ejectable liquid from a printhead, the printheadcomprising a plurality of nozzles;

a bubble forming chamber corresponding to each of the nozzlesrespectively, the bubble forming chambers adapted to contain a bubbleforming liquid; and,

at least one heater element disposed in each of the bubble formingchambers respectively, the heater elements configured for thermalcontact with the bubble forming liquid; wherein,

the bubble forming chamber has a circular cross section;

the method comprising the steps of:

placing the bubble forming liquid into thermal contact with the heaterelements; heating the heater elements to a temperature above the boilingpoint of the bubble forming liquid to form a gas bubble such that a dropof an ejectable liquid is ejected through the corresponding nozzle.

Preferably, the bubble forming chamber is cylindrical. In another form,the bubble forming chamber is barrel-shaped. In yet another embodiment,the bubble forming chamber is a truncated cone shape.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms that may fall within the scope of thepresent invention, related embodiments and preferred forms of theinvention will now be described, by way of example only, with referenceto the accompanying drawings in which:

FIGS. 1-3 illustrate the basic operational principles of a relatedembodiment using a thermal bend actuator;

FIG. 4 illustrates a three dimensional view of a single ink jet nozzlearrangement constructed in accordance with the related embodiment ofFIG. 1;

FIG. 5 illustrates an array of the nozzle arrangements of FIG. 4;

FIG. 6 shows a table to be used with reference to FIGS. 7 to 16;

FIGS. 7 to 16 show various stages in the manufacture of the ink jetnozzle arrangement of FIG. 4;

FIG. 17 is a schematic cross-sectional view through an ink chamber of aunit cell of a printhead according to a preferred embodiment of thepresent invention;

FIG. 18 is a schematic cross-sectional view through the ink chamber FIG.17, at another stage of operation;

FIG. 19 is a schematic cross-sectional view through the ink chamber FIG.17, at yet another stage of operation;

FIG. 20 is a schematic cross-sectional view through the ink chamber FIG.17, at yet a further stage of operation; and

FIG. 21 is a diagrammatic cross-sectional view through a unit cell of aprinthead in accordance with an embodiment of the invention showing thecollapse of a vapor bubble.

FIG. 22 is a schematic, partially cut away, perspective view of afurther embodiment of a unit cell of a printhead.

FIG. 23 is a schematic, partially cut away, exploded perspective view ofthe unit cell of FIG. 22.

FIG. 24 is a schematic, partially cut away, perspective view of afurther embodiment of a unit cell of a printhead.

FIG. 25 is a schematic, partially cut away, exploded perspective view ofthe unit cell of FIG. 24.

FIG. 26 is a schematic, partially cut away, perspective view of afurther embodiment of a unit cell of a printhead.

FIG. 27 is a schematic, partially cut away, exploded perspective view ofthe unit cell of FIG. 26.

FIG. 28 is a schematic, partially cut away, perspective view of afurther embodiment of a unit cell of a printhead.

FIG. 29 is a schematic, partially cut away, perspective view of afurther embodiment of a unit cell of a printhead.

FIG. 30 is a schematic, partially cut away, exploded perspective view ofthe unit cell of FIG. 29.

FIGS. 31 to 41 are schematic perspective views of the unit cell shown inFIGS. 29 and 30, at various successive stages in the production processof the printhead.

FIGS. 42 and 43 show schematic, partially cut away, schematicperspective views of two variations of the unit cell of FIGS. 29 to 41.

FIG. 44 is a schematic, partially cut away, perspective view of afurther embodiment of a unit cell of a printhead.

FIG. 45 is a schematic, partially cut away, perspective view of afurther embodiment of a unit cell of a printhead.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

Thermal Bend Actuator

In an embodiment related to the present invention, there is provided anozzle arrangement having a nozzle chamber containing ink and a thermalbend actuator connected to a paddle positioned within the chamber. Thethermal actuator device is actuated so as to eject ink from the nozzlechamber. The preferred embodiment includes a particular thermal bendactuator which includes a series of tapered portions for providingconductive heating of a conductive trace. The actuator is connected tothe paddle via an arm received through a slotted wall of the nozzlechamber. The actuator arm has a mating shape so as to mate substantiallywith the surfaces of the slot in the nozzle chamber wall.

Turning initially to FIG. 1-3, there is provided schematic illustrationsof the basic operation of a nozzle arrangement of this embodiment. Anozzle chamber 1 is provided filled with ink 2 by means of an ink inletchannel 3 which can be etched through a wafer substrate on which thenozzle chamber 1 rests. The nozzle chamber 1 further includes an inkejection port 4 around which an ink meniscus forms.

Inside the nozzle chamber 1 is a paddle type device 7 which isinterconnected to an actuator 8 through a slot in the wall of the nozzlechamber 1. The actuator 8 includes a heater means e.g. 9 locatedadjacent to an end portion of a post 10. The post 10 is fixed to asubstrate.

When it is desired to eject a drop from the nozzle chamber 1, asillustrated in FIG. 2, the heater means 9 is heated so as to undergothermal expansion. Preferably, the heater means 9 itself or the otherportions of the actuator 8 are built from materials having a high bendefficiency where the bend efficiency is defined as

${{bend}\mspace{14mu}{efficiency}} = \frac{{{Young}'}s\mspace{14mu}{Modulus} \times \left( {{Coefficient}\mspace{14mu}{of}\mspace{14mu}{thermal}\mspace{14mu}{Expansion}} \right)}{{Density} \times {Specific}\mspace{14mu}{Heat}\mspace{14mu}{Capacity}}$

A suitable material for the heater elements is a copper nickel alloywhich can be formed so as to bend a glass material.

The heater means 9 is ideally located adjacent the end portion of thepost 10 such that the effects of activation are magnified at the paddleend 7 such that small thermal expansions near the post 10 result inlarge movements of the paddle end.

The heater means 9 and consequential paddle movement causes a generalincrease in pressure around the ink meniscus 5 which expands, asillustrated in FIG. 2, in a rapid manner. The heater current is pulsedand ink is ejected out of the port 4 in addition to flowing in from theink channel 3.

Subsequently, the paddle 7 is deactivated to again return to itsquiescent position. The deactivation causes a general reflow of the inkinto the nozzle chamber. The forward momentum of the ink outside thenozzle rim and the corresponding backflow results in a general neckingand breaking off of the drop 12 which proceeds to the print media. Thecollapsed meniscus 5 results in a general sucking of ink into the nozzlechamber 2 via the ink flow channel 3. In time, the nozzle chamber 1 isrefilled such that the position in FIG. 1 is again reached and thenozzle chamber is subsequently ready for the ejection of another drop ofink.

FIG. 4 illustrates a side perspective view of the nozzle arrangementFIG. 5 illustrates sectional view through an array of nozzle arrangementof FIG. 4. In these figures, the numbering of elements previouslyintroduced has been retained.

Firstly, the actuator 8 includes a series of tapered actuator units e.g.15 which comprise an upper glass portion (amorphous silicon dioxide) 16formed on top of a titanium nitride layer 17. Alternatively a coppernickel alloy layer (hereinafter called cupronickel) can be utilizedwhich will have a higher bend efficiency where bend efficiency isdefined as:

${{bend}\mspace{14mu}{efficiency}} = \frac{{{Young}'}s\mspace{14mu}{Modulus} \times \left( {{Coefficient}\mspace{14mu}{of}\mspace{14mu}{thermal}\mspace{14mu}{Expansion}} \right)}{{Density} \times {Specific}\mspace{14mu}{Heat}\mspace{14mu}{Capacity}}$

The titanium nitride layer 17 is in a tapered form and, as such,resistive heating takes place near an end portion of the post 10.Adjacent titanium nitride/glass portions 15 are interconnected at ablock portion 19 which also provides a mechanical structural support forthe actuator 8.

The heater means 9 ideally includes a plurality of the tapered actuatorunit 15 which are elongate and spaced apart such that, upon heating, thebending force exhibited along the axis of the actuator 8 is maximized.Slots are defined between adjacent tapered units 15 and allow for slightdifferential operation of each actuator 8 with respect to adjacentactuators 8.

The block portion 19 is interconnected to an arm 20. The arm 20 is inturn connected to the paddle 7 inside the nozzle chamber 1 by means of aslot e.g. 22 formed in the side of the nozzle chamber 1. The slot 22 isdesigned generally to mate with the surfaces of the arm 20 so as tominimize opportunities for the outflow of ink around the arm 20. The inkis held generally within the nozzle chamber 1 via surface tensioneffects around the slot 22.

When it is desired to actuate the arm 20, a conductive current is passedthrough the titanium nitride layer 17 via vias within the block portion19 connecting to a lower CMOS layer 6 which provides the necessary powerand control circuitry for the nozzle arrangement. The conductive currentresults in heating of the nitride layer 17 adjacent to the post 10 whichresults in a general upward bending of the arm 20 and consequentialejection of ink out of the nozzle 4. The ejected drop is printed on apage in the usual manner for an inkjet printer as previously described.

An array of nozzle arrangements can be formed so as to create a singleprinthead. For example, in FIG. 5 there is illustrated a partlysectioned various array view which comprises multiple ink ejectionnozzle arrangements of FIG. 4 laid out in interleaved lines so as toform a printhead array. Of course, different types of arrays can beformulated including full color arrays etc.

The construction of the printhead system described can proceed utilizingstandard MEMS techniques through suitable modification of the steps asset out in U.S. Pat. No. 6,243,113 entitled “Image Creation Method andApparatus (IJ 41)” to the present applicant, the contents of which arefully incorporated by cross reference.

Fabrication of the ink jet nozzle arrangement is indicated in FIGS. 7 to16. The preferred embodiment achieves a particular balance betweenutilization of the standard semi-conductor processing material such astitanium nitride and glass in a MEMS process. The use of glass, orindeed any amorphous ceramic, to form the chamber is particularlybeneficial. The pressure transients within the chamber can exertsignificant stresses on the chamber wall. Amorphous ceramics arerelatively inexpensive and high strength, but also have anon-crystalline structure. Defects in a crystal structure can act asstress concentration points that are prone to failure in the cyclicalloading environment of the nozzle chambers.

Obviously the skilled person may make other choices of materials anddesign features where the economics are justified. For example, a coppernickel alloy of 50% copper and 50% nickel may be more advantageouslydeployed as the conductive heating compound as it is likely to havehigher levels of bend efficiency. Also, other design structures may beemployed where it is not necessary to provide for such a simple form ofmanufacture.

Bubble Forming Heater Element Actuator

The present invention is applicable to printheads using bubble formingheater elements. FIGS. 17 to 20 show a nozzle of this type. While thefabrication of nozzles of this type is described below, the nozzles,ejection actuators, associated drive circuitry and ink supply passagesis formed on and through a wafer using lithographically masked etchingtechniques described in great detail in U.S. Ser. No. 10/302,274. In theinterests of brevity, the disclosure of the '274 application isincorporated herein in its entirety.

With reference to FIGS. 17 to 20, the unit cell 1 of a printheadaccording to an embodiment of the invention comprises a nozzle plate 2with nozzles 3 therein, the nozzles having nozzle rims 4, and apertures5 extending through the nozzle plate. The nozzle plate 2 is plasmaetched from a silicon nitride structure which is deposited, by way ofchemical vapor deposition (CVD), over a sacrificial material which issubsequently etched.

The printhead also includes, with respect to each nozzle 3, side walls 6on which the nozzle plate is supported, a chamber 7 defined by the wallsand the nozzle plate 2, a multi-layer substrate 8 and an inlet passage 9extending through the multi-layer substrate to the far side (not shown)of the substrate. A looped, elongate heater element 10 is suspendedwithin the chamber 7, so that the element is in the form of a suspendedbeam. The printhead as shown is a microelectromechanical system (MEMS)structure, which is formed by a lithographic process which is describedin more detail below.

When the printhead is in use, ink 11 from a reservoir (not shown) entersthe chamber 7 via the inlet passage 9, so that the chamber fills to thelevel as shown in FIG. 17. Thereafter, the heater element 10 is heatedfor somewhat less than 1 microsecond, so that the heating is in the formof a thermal pulse. It will be appreciated that the heater element 10 isin thermal contact with the ink 11 in the chamber 7 so that when theelement is heated, this causes the generation of vapor bubbles 12 in theink. Accordingly, the ink 11 constitutes a bubble forming liquid. FIG.17 shows the formation of a bubble 12 approximately 1 microsecond aftergeneration of the thermal pulse, that is, when the bubble has justnucleated on the heater elements 10. It will be appreciated that, as theheat is applied in the form of a pulse, all the energy necessary togenerate the bubble 12 is to be supplied within that short time.

When the element 10 is heated as described above, the bubble 12 formsalong the length of the element, this bubble appearing, in thecross-sectional view of FIG. 17, as four bubble portions, one for eachof the element portions shown in cross section.

The bubble 12, once generated, causes an increase in pressure within thechamber 7, which in turn causes the ejection of a drop 16 of the ink 11through the nozzle 3. The rim 4 assists in directing the drop 16 as itis ejected, so as to minimize the chance of drop misdirection.

The reason that there is only one nozzle 3 and chamber 7 per inletpassage 9 is so that the pressure wave generated within the chamber, onheating of the element 10 and forming of a bubble 12, does not affectadjacent chambers and their corresponding nozzles. As discussed above inrelation to the related embodiment, the pressure wave generated withinthe chamber creates significant stresses in the chamber wall. Bydesigning the chamber 7 with a circular cross section, it has muchgreater structural strength and rigidity. The circular geometry avoidsstress concentration points that weaken the structure and may eventuallylead to failure. The use of an inherently high strength structure allowsthe use of less material that in turn provides a more compact and agreater nozzle density on the printhead. This in turn improves theprinting resolution. Furthermore, forming the chamber from an amorphousceramic such as silicon nitride, silicon dioxide (glass) or siliconoxynitride, gives the chamber walls high strength while avoiding the useof material with a crystal structure. Crystalline defects can act asstress concentration points and therefore potential areas of weaknessand ultimately failure.

FIGS. 18 and 19 show the unit cell 1 at two successive later stages ofoperation of the printhead. It can be seen that the bubble 12 generatesfurther, and hence grows, with the resultant advancement of ink 11through the nozzle 3. The shape of the bubble 12 as it grows, as shownin FIG. 3, is determined by a combination of the inertial dynamics andthe surface tension of the ink 11. The surface tension tends to minimizethe surface area of the bubble 12 so that, by the time a certain amountof liquid has evaporated, the bubble is essentially disk-shaped.

The increase in pressure within the chamber 7 not only pushes ink 11 outthrough the nozzle 3, but also pushes some ink back through the inletpassage 9. However, the inlet passage 9 is approximately 200 to 300microns in length, and is only approximately 16 microns in diameter.Hence there is a substantial viscous drag. As a result, the predominanteffect of the pressure rise in the chamber 7 is to force ink out throughthe nozzle 3 as an ejected drop 16, rather than back through the inletpassage 9.

Turning now to FIG. 20, the printhead is shown at a still furthersuccessive stage of operation, in which the ink drop 16 that is beingejected is shown during its “necking phase” before the drop breaks off.At this stage, the bubble 12 has already reached its maximum size andhas then begun to collapse towards the point of collapse 17, asreflected in more detail in FIG. 21.

The collapsing of the bubble 12 towards the point of collapse 17 causessome ink 11 to be drawn from within the nozzle 3 (from the sides 18 ofthe drop), and some to be drawn from the inlet passage 9, towards thepoint of collapse. Most of the ink 11 drawn in this manner is drawn fromthe nozzle 3, forming an annular neck 19 at the base of the drop 16prior to its breaking off.

The drop 16 requires a certain amount of momentum to overcome surfacetension forces, in order to break off. As ink 11 is drawn from thenozzle 3 by the collapse of the bubble 12, the diameter of the neck 19reduces thereby reducing the amount of total surface tension holding thedrop, so that the momentum of the drop as it is ejected out of thenozzle is sufficient to allow the drop to break off.

When the drop 16 breaks off, cavitation forces are caused as reflectedby the arrows 20, as the bubble 12 collapses to the point of collapse17. It will be noted that there are no solid surfaces in the vicinity ofthe point of collapse 17 on which the cavitation can have an effect.

Features and Advantages of Further Embodiments

FIGS. 22 to 45 show further embodiments of unit cells 1 for thermalinkjet printheads, each embodiment having its own particular functionaladvantages. These advantages will be discussed in detail below, withreference to each individual embodiment. However, the basic constructionof each embodiment is best shown in FIGS. 23, 25, 27 and 30. Themanufacturing process is substantially the same as that described abovein relation to FIGS. 6 to 31 of the above referenced U.S. Ser. No.10/302,274 (incorporated herein by cross reference). For consistency,the same reference numerals are used in FIGS. 22 to 45 to indicatecorresponding components. In the interests of brevity, the fabricationstages have been shown for the unit cell of FIG. 29 only (see FIGS. 31to 41). It will be appreciated that the other unit cells will use thesame fabrication stages with different masking. Again, the deposition ofsuccessive layers shown in FIGS. 31 to 41 need not be described indetail below given that the lithographic process largely corresponds tothat shown in FIGS. 6 to 31 in U.S. Ser. No. 10/302,274.

Referring to FIGS. 22 and 23, the unit cell 1 shown has the chamber 7,ink supply passage 32 and the nozzle rim 4 positioned mid way along thelength of the unit cell 1. As best seen in FIG. 23, the drive circuitryis partially on one side of the chamber 7 with the remainder on theopposing side of the chamber. The drive circuitry 22 controls theoperation of the heater 14 through vias in the integrated circuitmetallisation layers of the interconnect 23. The interconnect 23 has araised metal layer on its top surface. Passivation layer 24 is formed intop of the interconnect 23 but leaves areas of the raised metal layerexposed. Electrodes 15 of the heater 14 contact the exposed metal areasto supply power to the element 10.

Alternatively, the drive circuitry 22 for one unit cell is not onopposing sides of the heater element that it controls. All the drivecircuitry 22 for the heater 14 of one unit cell is in a single,undivided area that is offset from the heater. That is, the drivecircuitry 22 is partially overlaid by one of the electrodes 15 of theheater 14 that it is controlling, and partially overlaid by one or moreof the heater electrodes 15 from adjacent unit cells. In this situation,the center of the drive circuitry 22 is less than 200 microns from thecenter of the associate nozzle aperture 5. In most Memjet printheads ofthis type, the offset is less than 100 microns and in many cases lessthan 50 microns, preferably less than 30 microns.

Configuring the nozzle components so that there is significant overlapbetween the electrodes and the drive circuitry provides a compact designwith high nozzle density (nozzles per unit area of the nozzle plate 2).This also improves the efficiency of the printhead by shortening thelength of the conductors from the circuitry to the electrodes. Theshorter conductors have less resistance and therefore dissipate lessenergy.

The high degree of overlap between the electrodes 15 and the drivecircuitry 22 also allows more vias between the heater material and theCMOS metalization layers of the interconnect 23. As best shown in FIGS.30 and 31, the passivation layer 24 has an array of vias to establish anelectrical connection with the heater 14. More vias lowers theresistance between the heater electrodes 15 and the interconnect layer23 which reduces power losses.

In FIGS. 24 and 25, the unit cell 1 is the same as that of FIGS. 22 and23 apart from the heater element 10. The heater element 10 has a bubblenucleation section 158 with a smaller cross section than the remainderof the element. The bubble nucleation section 158 has a greaterresistance and heats to a temperature above the boiling point of the inkbefore the remainder of the element 10. The gas bubble nucleates at thisregion and subsequently grows to surround the rest of the element 10. Bycontrolling the bubble nucleation and growth, the trajectory of theejected drop is more predictable.

The heater element 10 is configured to accommodate thermal expansion ina specific manner. As heater elements expand, they will deform torelieve the strain. Elements such as that shown in FIGS. 22 and 23 willbow out of the plane of lamination because its thickness is the thinnestcross sectional dimension and therefore has the least bendingresistance. Repeated bending of the element can lead to the formation ofcracks, especially at sharp corners, which can ultimately lead tofailure. The heater element 10 shown in FIGS. 24 and 25 is configured sothat the thermal expansion is relieved by rotation of the bubblenucleation section 158, and slightly splaying the sections leading tothe electrodes 15, in preference to bowing out of the plane oflamination. The geometry of the element is such that miniscule bendingwithin the plane of lamination is sufficient to relieve the strain ofthermal expansion, and such bending occurs in preference to bowing. Thisgives the heater element greater longevity and reliability by minimizingbend regions, which are prone to oxidation and cracking

Referring to FIGS. 26 and 27, the heater element 10 used in this unitcell 1 has a serpentine or ‘double omega’ shape. This configurationkeeps the gas bubble centered on the axis of the nozzle. A single omegais a simple geometric shape which is beneficial from a fabricationperspective. However the gap 159 between the ends of the heater elementmeans that the heating of the ink in the chamber is slightlyasymmetrical. As a result, the gas bubble is slightly skewed to the sideopposite the gap 159. This can in turn affect the trajectory of theejected drop. The double omega shape provides the heater element withthe gap 160 to compensate for the gap 159 so that the symmetry andposition of the bubble within the chamber is better controlled and theejected drop trajectory is more reliable.

FIG. 28 shows a heater element 10 with a single omega shape. Asdiscussed above, the simplicity of this shape has significant advantagesduring lithographic fabrication. It can be a single current path that isrelatively wide and therefore less affected by any inherent inaccuraciesin the deposition of the heater material. The inherent inaccuracies ofthe equipment used to deposit the heater material result in variationsin the dimensions of the element. However, these tolerances are fixedvalues so the resulting variations in the dimensions of a relativelywide component are proportionally less than the variations for a thinnercomponent. It will be appreciated that proportionally large changes ofcomponents dimensions will have a greater effect on their intendedfunction. Therefore the performance characteristics of a relatively wideheater element are more reliable than a thinner one.

The omega shape directs current flow around the axis of the nozzleaperture 5. This gives good bubble alignment with the aperture forbetter ejection of drops while ensuring that the bubble collapse pointis not on the heater element 10. As discussed above, this avoidsproblems caused by cavitation.

Referring to FIGS. 29 to 42, another embodiment of the unit cell 1 isshown together with several stages of the etching and depositionfabrication process. In this embodiment, the heater element 10 issuspended from opposing sides of the chamber. This allows it to besymmetrical about two planes that intersect along the axis of the nozzleaperture 5. This configuration provides a drop trajectory along the axisof the nozzle aperture 5 while avoiding the cavitation problemsdiscussed above. FIGS. 43 and 44 show other variations of this type ofheater element 10.

FIG. 44 shows a unit cell 1 that has the nozzle aperture 5 and theheater element 10 offset from the center of the nozzle chamber 7.Consequently, the nozzle chamber 7 is larger than the previousembodiments. The heater 14 has two different electrodes 15 with theright hand electrode 15 extending well into the nozzle chamber 7 tosupport one side of the heater element 10. This reduces the area of thevias contacting the electrodes which can increase the electroderesistance and therefore the power losses. However, laterally offsettingthe heater element from the ink inlet 31 increases the fluidic dragretarding flow back through the inlet 31 and ink supply passage 32. Thefluidic drag through the nozzle aperture 5 comparatively much smaller solittle energy is lost to a reverse flow of ink through the inlet when agas bubble form on the element 10.

The unit cell 1 shown in FIG. 45 also has a relatively large chamber 7which again reduces the surface area of the electrodes in contact withthe vias leading to the interconnect layer 23. However, the largerchamber 7 allows several heater elements 10 offset from the nozzleaperture 5. The arrangement shown uses two heater elements 10; one oneither side of the chamber 7. Other designs use three or more elementsin the chamber. Gas bubbles nucleate from opposing sides of the nozzleaperture and converge to form a single bubble. The bubble formed issymmetrical about at least one plane extending along the nozzle axis.This enhances the control of the symmetry and position of the bubblewithin the chamber 7 and therefore the ejected drop trajectory is morereliable.

Other Embodiments

The invention has been described above with reference to printheadsusing thermal bend actuators and bubble forming heater elements.However, it is potentially suited to a wide range of printing systemincluding: color and monochrome office printers, short run digitalprinters, high speed digital printers, offset press supplementalprinters, low cost scanning printers high speed pagewidth printers,notebook computers with inbuilt pagewidth printers, portable color andmonochrome printers, color and monochrome copiers, color and monochromefacsimile machines, combined printer, facsimile and copying machines,label printers, large format plotters, photograph copiers, printers fordigital photographic “minilabs”, video printers, PHOTO CD (PHOTO CD is aregistered trade mark of the Eastman Kodak Company) printers, portableprinters for PDAs, wallpaper printers, indoor sign printers, billboardprinters, fabric printers, camera printers and fault tolerant commercialprinter arrays.

It will be appreciated by ordinary workers in this field that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Ofcourse many different devices could be used. However presently popularink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal ink jet is power consumption.This is approximately 100 times that required for high speed, and stemsfrom the energy-inefficient means of drop ejection. This involves therapid boiling of water to produce a vapor bubble which expels the ink.Water has a very high heat capacity, and must be superheated in thermalink jet applications. In conventional thermal inkjet printheads, thisleads to an efficiency of around 0.02%, from electricity input to dropmomentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size andcost. Piezoelectric crystals have a very small deflection at reasonabledrive voltages, and therefore require a large area for each nozzle.Also, each piezoelectric actuator must be connected to its drive circuiton a separate substrate. This is not a significant problem at thecurrent limit of around 300 nozzles per printhead, but is a majorimpediment to the fabrication of pagewidth printheads with 19,200nozzles.

Ideally, the ink jet technologies used meet the stringent requirementsof in-camera digital color printing and other high quality, high speed,low cost printing applications. To meet the requirements of digitalphotography, new ink jet technologies have been created. The targetfeatures include:

low power (less than 10 Watts)

high resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the ink jet systemsdescribed below with differing levels of difficulty. Forty-fivedifferent ink jet technologies have been developed by the Assignee togive a wide range of choices for high volume manufacture. Thesetechnologies form part of separate applications assigned to the presentAssignee as set out in the table under the heading Cross References toRelated Applications.

The ink jet designs shown here are suitable for a wide range of digitalprinting systems, from battery powered one-time use digital cameras,through to desktop and network printers, and through to commercialprinting systems.

For ease of manufacture using standard process equipment, the printheadis designed to be a monolithic 0.5 micron CMOS chip with MEMS postprocessing. For color photographic applications, the printhead is 100 mmlong, with a width which depends upon the ink jet type. The smallestprinthead designed is IJ38, which is 0.35 mm wide, giving a chip area of35 square mm. The printheads each contain 19,200 nozzles plus data andcontrol circuitry.

Ink is supplied to the back of the printhead by injection molded plasticink channels. The molding requires 50 micron features, which can becreated using a lithographically micromachined insert in a standardinjection molding tool. Ink flows through holes etched through the waferto the nozzle chambers fabricated on the front surface of the wafer. Theprinthead is connected to the camera circuitry by tape automatedbonding.

Tables of Drop-on-Demand Ink Jets

Eleven important characteristics of the fundamental operation ofindividual ink jet nozzles have been identified. These characteristicsare largely orthogonal, and so can be elucidated as an elevendimensional matrix. Most of the eleven axes of this matrix includeentries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of inkjet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types)

Nozzle clearing method (9 types)

Nozzle plate construction (9 types)

Drop ejection direction (5 types)

Ink type (7 types)

The complete eleven dimensional table represented by these axes contains36.9 billion possible configurations of ink jet nozzle. While not all ofthe possible combinations result in a viable ink jet technology, manymillion configurations are viable. It is clearly impractical toelucidate all of the possible configurations. Instead, certain ink jettypes have been investigated in detail. These are designated IJ01 toIJ45 above which matches the docket numbers in the table under theheading Cross References to Related Applications.

Other ink jet configurations can readily be derived from theseforty-five examples by substituting alternative configurations along oneor more of the 11 axes. Most of the IJ01 to IJ45 examples can be madeinto ink jet printheads with characteristics superior to any currentlyavailable ink jet technology.

Where there are prior art examples known to the inventor, one or more ofthese examples are listed in the examples column of the tables below.The IJ01 to IJ45 series are also listed in the examples column. In somecases, print technology may be listed more than once in a table, whereit shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Homeprinters, Office network printers, Short run digital printers,Commercial print systems, Fabric printers, Pocket printers, Internet WWWprinters, Video printers, Medical imaging, Wide format printers,Notebook PC printers, Fax machines, Industrial printing systems,Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrixare set out in the following tables.

ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS) DescriptionAdvantages Disadvantages Examples Thermal An electrothermal Large forceHigh power Canon bubble heater heats the generated Ink carrier Bubblejet1979 ink to above Simple limited to water Endo et al GB boiling point,construction Low patent 2,007,162 transferring No moving efficiencyXerox heater- significant heat to parts High in-pit 1990 the aqueousink. A Fast operation temperatures Hawkins et al bubble nucleates Smallchip required U.S. Pat. No. 4,899,181 and quickly forms, area requiredfor High Hewlett- expelling the ink. actuator mechanical Packard TIJ Theefficiency of stress 1982 Vaught et the process is low, Unusual al U.S.Pat. No. with typically less materials 4,490,728 than 0.05% of therequired electrical energy Large drive being transformed transistorsinto kinetic energy Cavitation of the drop. causes actuator failureKogation reduces bubble formation Large print heads are difficult tofabricate Piezo- A piezoelectric Low power Very large Kyser et alelectric crystal such as consumption area required for U.S. Pat. No.3,946,398 lead lanthanum Many ink actuator Zoltan U.S. Pat. No.zirconate (PZT) is types can be Difficult to 3,683,212 electrically usedintegrate with 1973 Stemme activated, and Fast operation electronicsU.S. Pat. No. 3,747,120 either expands, High High voltage Epson Stylusshears, or bends to efficiency drive transistors Tektronix applypressure to required IJ04 the ink, ejecting Full drops. pagewidth printheads impractical due to actuator size Requires electrical poling inhigh field strengths during manufacture Electro- An electric field isLow power Low Seiko Epson, strictive used to activate consumptionmaximum strain Usui et all JP electrostriction in Many ink (approx.0.01%) 253401/96 relaxor materials types can be Large area IJ04 such aslead used required for lanthanum Low thermal actuator due to zirconatetitanate expansion low strain (PLZT) or lead Electric field Responsemagnesium strength required speed is niobate (PMN). (approx. 3.5 V/μm)marginal (~ 10 μs) can be High voltage generated drive transistorswithout required difficulty Full Does not pagewidth print requireelectrical heads poling impractical due to actuator size Ferro- Anelectric field is Low power Difficult to IJ04 electric used to induce aconsumption integrate with phase transition Many ink electronics betweenthe types can be Unusual antiferroelectric used materials such as (AFE)and Fast operation PLZSnT are ferroelectric (FE) (<1 μs) required phase.Perovskite Relatively Actuators materials such as high longitudinalrequire a large tin modified lead strain area lanthanum High zirconatetitanate efficiency (PLZSnT) exhibit Electric field large strains of upstrength of to 1% associated around 3 V/μm with the AFE to can bereadily FE phase provided transition. Electro- Conductive plates Lowpower Difficult to IJ02, IJ04 static are separated by a consumptionoperate plates compressible or Many ink electrostatic fluid dielectrictypes can be devices in an (usually air). Upon used aqueous applicationof a Fast operation environment voltage, the plates The attract eachother electrostatic and displace ink, actuator will causing dropnormally need to ejection. The be separated conductive plates from theink may be in a comb Very large or honeycomb area required to structure,or achieve high stacked to increase forces the surface area High voltageand therefore the drive transistors force. may be required Fullpagewidth print heads are not competitive due to actuator size Electro-A strong electric Low current High voltage 1989 Saito et static pullfield is applied to consumption required al, U.S. Pat. No. on ink theink, whereupon Low May be 4,799,068 electrostatic temperature damaged by1989 Miura et attraction sparks due to air al, U.S. Pat. No. acceleratesthe ink breakdown 4,810,954 towards the print Required field Tone-jetmedium. strength increases as the drop size decreases High voltage drivetransistors required Electrostatic field attracts dust Permanent Anelectromagnet Low power Complex IJ07, IJ10 magnet directly attracts aconsumption fabrication electro- permanent magnet, Many ink Permanentmagnetic displacing ink and types can be magnetic causing drop usedmaterial such as ejection. Rare Fast operation Neodymium Iron earthmagnets with High Boron (NdFeB) a field strength efficiency required.around 1 Tesla can Easy High local be used. Examples extension fromcurrents required are: Samarium single nozzles to Copper Cobalt (SaCo)and pagewidth print metalization magnetic materials heads should be usedin the neodymium for long iron boron family electromigration (NdFeB,lifetime and low NdDyFeBNb, resistivity NdDyFeB, etc) Pigmented inks areusually infeasible Operating temperature limited to the Curietemperature (around 540 K) Soft A solenoid Low power Complex IJ01, IJ05,magnetic induced a consumption fabrication IJ08, IJ10, IJ12, coremagnetic field in a Many ink Materials not IJ14, IJ15, IJ17 electro-soft magnetic core types can be usually present magnetic or yokefabricated used in a CMOS fab from a ferrous Fast operation such asNiFe, material such as High CoNiFe, or CoFe electroplated ironefficiency are required alloys such as Easy High local CoNiFe [1], CoFe,extension from currents required or NiFe alloys. single nozzles toCopper Typically, the soft pagewidth print metalization magneticmaterial heads should be used is in two parts, for long which areelectromigration normally held lifetime and low apart by a spring.resistivity When the solenoid Electroplating is actuated, the two isrequired parts attract, High displacing the ink. saturation flux densityis required (2.0-2.1 T is achievable with CoNiFe [1]) Lorenz The Lorenzforce Low power Force acts as a IJ06, IJ11, force acting on a currentconsumption twisting motion IJ13, IJ16 carrying wire in a Many inkTypically, magnetic field is types can be only a quarter of utilized.used the solenoid This allows the Fast operation length providesmagnetic field to High force in a useful be supplied efficiencydirection externally to the Easy High local print head, for extensionfrom currents required example with rare single nozzles to Copper earthpermanent pagewidth print metalization magnets. heads should be usedOnly the current for long carrying wire need electromigration befabricated on lifetime and low the print-head, resistivity simplifyingPigmented materials inks are usually requirements. infeasible Magneto-The actuator uses Many ink Force acts as a Fischenbeck, striction thegiant types can be twisting motion U.S. Pat. No. 4,032,929magnetostrictive used Unusual IJ25 effect of materials Fast operationmaterials such as such as Terfenol-D Easy Terfenol-D are (an alloy ofextension from required terbium, single nozzles to High local dysprosiumand pagewidth print currents required iron developed at heads Copper theNaval High force is metalization Ordnance available should be usedLaboratory, hence for long Ter-Fe-NOL). For electromigration bestefficiency, the lifetime and low actuator should be resistivitypre-stressed to Pre-stressing approx. 8 MPa. may be required Surface Inkunder positive Low power Requires Silverbrook, tension pressure is heldin consumption supplementary EP 0771 658 A2 reduction a nozzle bysurface Simple force to effect and related tension. The constructiondrop separation patent surface tension of No unusual Requiresapplications the ink is reduced materials special ink below the bubblerequired in surfactants threshold, causing fabrication Speed may be theink to egress High limited by from the nozzle. efficiency surfactantEasy properties extension from single nozzles to pagewidth print headsViscosity The ink viscosity Simple Requires Silverbrook, reduction islocally reduced construction supplementary EP 0771 658 A2 to selectwhich No unusual force to effect and related drops are to be materialsdrop separation patent ejected. A required in Requires applicationsviscosity reduction fabrication special ink can be achieved Easyviscosity electrothermally extension from properties with most inks, butsingle nozzles to High speed is special inks can be pagewidth printdifficult to engineered for a heads achieve 100:1 viscosity Requiresreduction. oscillating ink pressure A high temperature difference(typically 80 degrees) is required Acoustic An acoustic wave Can operateComplex 1993 is generated and without a nozzle drive circuitryHadimioglu et focussed upon the plate Complex al, EUP 550,192 dropejection fabrication 1993 Elrod et region. Low al, EUP 572,220efficiency Poor control of drop position Poor control of drop volumeThermo- An actuator which Low power Efficient IJ03, IJ09, elastic reliesupon consumption aqueous IJ17, IJ18, IJ19, bend differential Many inkoperation IJ20, IJ21, IJ22, actuator thermal expansion types can berequires a IJ23, IJ24, IJ27, upon Joule heating used thermal insulatorIJ28, IJ29, IJ30, is used. Simple planar on the hot side IJ31, IJ32,IJ33, fabrication Corrosion IJ34, IJ35, IJ36, Small chip prevention canIJ37, IJ38, IJ39, area required for be difficult IJ40, IJ41 eachactuator Pigmented Fast operation inks may be High infeasible, asefficiency pigment particles CMOS may jam the compatible bend actuatorvoltages and currents Standard MEMS processes can be used Easy extensionfrom single nozzles to pagewidth print heads High CTE A material with aHigh force Requires IJ09, IJ17, thermo- very high can be generatedspecial material IJ18, IJ20, IJ21, elastic coefficient of Three (e.g.PTFE) IJ22, IJ23, IJ24, actuator thermal expansion methods of Requires aIJ27, IJ28, IJ29, (CTE) such as PTFE deposition PTFE deposition IJ30,IJ31, IJ42, polytetrafluoroethylene are under process, which is IJ43,IJ44 (PTFE) is development: not yet standard used. As high CTE chemicalvapor in ULSI fabs materials are deposition PTFE usually non- (CVD),spin deposition conductive, a coating, and cannot be heater fabricatedevaporation followed with from a conductive PTFE is a high temperaturematerial is candidate for (above 350° C.) incorporated. A 50 μm lowdielectric processing long PTFE constant Pigmented bend actuator withinsulation in inks may be polysilicon heater ULSI infeasible, as and 15mW power Very low pigment particles input can provide power may jam the180 μN force and consumption bend actuator 10 μm deflection. Many inkActuator motions types can be include: used Bend Simple planar Pushfabrication Buckle Small chip Rotate area required for each actuatorFast operation High efficiency CMOS compatible voltages and currentsEasy extension from single nozzles to pagewidth print heads Conductive Apolymer with a High force Requires IJ24 polymer high coefficient of canbe generated special materials thermo- thermal expansion Very lowdevelopment elastic (such as PTFE) is power (High CTE actuator dopedwith consumption conductive conducting Many ink polymer) substances totypes can be Requires a increase its used PTFE deposition conductivityto Simple planar process, which is about 3 orders of fabrication not yetstandard magnitude below Small chip in ULSI fabs that of copper. Thearea required for PTFE conducting each actuator deposition polymerexpands Fast operation cannot be when resistively High followed withheated. efficiency high temperature Examples of CMOS (above 350° C.)conducting compatible processing dopants include: voltages andEvaporation Carbon nanotubes currents and CVD Metal fibers Easydeposition Conductive extension from techniques polymers such as singlenozzles to cannot be used doped pagewidth print Pigmented polythiopheneheads inks may be Carbon granules infeasible, as pigment particles mayjam the bend actuator Shape A shape memory High force is Fatigue limitsIJ26 memory alloy such as TiNi available maximum alloy (also known as(stresses of number of cycles Nitinol —Nickel hundreds of Low strainTitanium alloy MPa) (1%) is required developed at the Large strain is toextend fatigue Naval Ordnance available (more resistance Laboratory) isthan 3%) Cycle rate thermally switched High limited by heat between itsweak corrosion removal martensitic state resistance Requires and itshigh Simple unusual stiffness austenic construction materials (TiNi)state. The shape of Easy The latent the actuator in its extension fromheat of martensitic state is single nozzles to transformation deformedrelative pagewidth print must be to the austenic heads provided shape.The shape Low voltage High current change causes operation operationejection of a drop. Requires pre- stressing to distort the martensiticstate Linear Linear magnetic Linear Requires IJ12 Magnetic actuatorsinclude Magnetic unusual Actuator the Linear actuators can besemiconductor Induction Actuator constructed with materials such as(LIA), Linear high thrust, long soft magnetic Permanent Magnet travel,and high alloys (e.g. Synchronous efficiency using CoNiFe) Actuatorplanar Some varieties (LPMSA), Linear semiconductor also requireReluctance fabrication permanent Synchronous techniques magneticActuator (LRSA), Long actuator materials such as Linear Switched travelis Neodymium iron Reluctance available boron (NdFeB) Actuator (LSRA),Medium force Requires and the Linear is available complex multi- StepperActuator Low voltage phase drive (LSA). operation circuitry High currentoperation

BASIC OPERATION MODE Description Advantages Disadvantages ExamplesActuator This is the Simple Drop Thermal ink directly simplest mode ofoperation repetition rate is jet pushes operation: the No externalusually limited Piezoelectric ink actuator directly fields required toaround 10 kHz. ink jet supplies sufficient Satellite drops However,IJ01, IJ02, kinetic energy to can be avoided if this is not IJ03, IJ04,IJ05, expel the drop. drop velocity is fundamental to IJ06, IJ07, IJ09,The drop must less than 4 m/s the method, but IJ11, IJ12, IJ14, have asufficient Can be is related to the IJ16, IJ20, IJ22, velocity toefficient, refill method IJ23, IJ24, IJ25, overcome the depending uponnormally used IJ26, IJ27, IJ28, surface tension. the actuator used Allof the drop IJ29, IJ30, IJ31, kinetic energy IJ32, IJ33, IJ34, must beIJ35, IJ36, IJ37, provided by the IJ38, IJ39, IJ40, actuator IJ41, IJ42,IJ43, Satellite drops IJ44 usually form if drop velocity is greater than4.5 m/s Proximity The drops to be Very simple Requires closeSilverbrook, printed are print head proximity EP 0771 658 A2 selected bysome fabrication can between the and related manner (e.g. be used printhead and patent thermally induced The drop the print media applicationssurface tension selection means or transfer roller reduction of does notneed to May require pressurized ink). provide the two print headsSelected drops are energy required printing alternate separated from theto separate the rows of the ink in the nozzle drop from the image bycontact with the nozzle Monolithic print medium or a color print headstransfer roller. are difficult Electrostatic The drops to be Very simpleRequires very Silverbrook, pull printed are print head highelectrostatic EP 0771 658 A2 on ink selected by some fabrication canfield and related manner (e.g. be used Electrostatic patent thermallyinduced The drop field for small applications surface tension selectionmeans nozzle sizes is Tone-Jet reduction of does not need to above airpressurized ink). provide the breakdown Selected drops are energyrequired Electrostatic separated from the to separate the field mayattract ink in the nozzle drop from the dust by a strong electric nozzlefield. Magnetic The drops to be Very simple Requires Silverbrook, pullon printed are print head magnetic ink EP 0771 658 A2 ink selected bysome fabrication can Ink colors and related manner (e.g. be used otherthan black patent thermally induced The drop are difficult applicationssurface tension selection means Requires very reduction of does not needto high magnetic pressurized ink). provide the fields Selected drops areenergy required separated from the to separate the ink in the nozzledrop from the by a strong nozzle magnetic field acting on the magneticink. Shutter The actuator High speed Moving parts IJ13, IJ17, moves ashutter to (>50 kHz) are required IJ21 block ink flow to operation canbe Requires ink the nozzle. The ink achieved due to pressure pressure ispulsed reduced refill modulator at a multiple of the time Friction anddrop ejection Drop timing wear must be frequency. can be very consideredaccurate Stiction is The actuator possible energy can be very lowShuttered The actuator Actuators with Moving parts IJ08, IJ15, grillmoves a shutter to small travel can are required IJ18, IJ19 block inkflow be used Requires ink through a grill to Actuators with pressure thenozzle. The small force can modulator shutter movement be used Frictionand need only be equal High speed wear must be to the width of the (>50kHz) considered grill holes. operation can be Stiction is achievedpossible Pulsed A pulsed magnetic Extremely low Requires an IJ10magnetic field attracts an energy operation external pulsed pull on ‘inkpusher’ at the is possible magnetic field ink drop ejection No heatRequires pusher frequency. An dissipation special materials actuatorcontrols a problems for both the catch, which actuator and the preventsthe ink ink pusher pusher from Complex moving when a construction dropis not to be ejected.

AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES) Description AdvantagesDisadvantages Examples None The actuator Simplicity of Drop ejectionMost ink jets, directly fires the construction energy must be includingink drop, and there Simplicity of supplied by piezoelectric and is noexternal field operation individual nozzle thermal bubble. or otherSmall physical actuator IJ01, IJ02, mechanism size IJ03, IJ04, IJ05,required. IJ07, IJ09, IJ11, IJ12, IJ14, IJ20, IJ22, IJ23, IJ24, IJ25,IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, IJ36, IJ37,IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Oscillating The ink pressureOscillating ink Requires Silverbrook, ink oscillates, pressure canexternal ink EP 0771 658 A2 pressure providing much of provide a refillpressure and related (including the drop ejection pulse, allowingoscillator patent acoustic energy. The higher operating Ink pressureapplications stimulation) actuator selects speed phase and IJ08, IJ13,which drops are to The actuators amplitude must IJ15, IJ17, IJ18, befired by may operate be carefully IJ19, IJ21 selectively with much lowercontrolled blocking or energy Acoustic enabling nozzles. Acousticreflections in the The ink pressure lenses can be ink chamberoscillation may be used to focus the must be achieved by sound on thedesigned for vibrating the print nozzles head, or preferably by anactuator in the ink supply. Media The print head is Low power PrecisionSilverbrook, proximity placed in close High accuracy assembly EP 0771658 A2 proximity to the Simple print required and related print medium.head Paper fibers patent Selected drops construction may causeapplications protrude from the problems print head further Cannot printthan unselected on rough drops, and contact substrates the print medium.The drop soaks into the medium fast enough to cause drop separation.Transfer Drops are printed High accuracy Bulky Silverbrook, roller to atransfer roller Wide range of Expensive EP 0771 658 A2 instead ofstraight print substrates Complex and related to the print can be usedconstruction patent medium. A Ink can be applications transfer rollercan dried on the Tektronix hot also be used for transfer roller meltproximity drop piezoelectric ink separation. jet Any of the IJ seriesElectro- An electric field is Low power Field strength Silverbrook,static used to accelerate Simple print required for EP 0771 658 A2selected drops head separation of and related towards the printconstruction small drops is patent medium. near or above airapplications breakdown Tone-Jet Direct A magnetic field is Low powerRequires Silverbrook, magnetic used to accelerate Simple print magneticink EP 0771 658 A2 field selected drops of head Requires and relatedmagnetic ink construction strong magnetic patent towards the print fieldapplications medium. Cross The print head is Does not Requires IJ06,IJ16 magnetic placed in a require magnetic external magnet fieldconstant magnetic materials to be Current field. The Lorenz integratedin the densities may be force in a current print head high, resulting incarrying wire is manufacturing electromigration used to move the processproblems actuator. Pulsed A pulsed magnetic Very low Complex print IJ10magnetic field is used to power operation head field cyclically attracta is possible construction paddle, which Small print Magnetic pushes onthe ink. head size materials A small actuator required in print moves acatch, head which selectively prevents the paddle from moving.

ACTUATOR AMPLIFICATION OR MODIFICATION METHOD Description AdvantagesDisadvantages Examples None No actuator Operational Many actuatorThermal mechanical simplicity mechanisms Bubble Ink jet amplification ishave insufficient IJ01, IJ02, used. The actuator travel, or IJ06, IJ07,IJ16, directly drives the insufficient IJ25, IJ26 drop ejection force,to process. efficiently drive the drop ejection process Differential Anactuator Provides High stresses Piezoelectric expansion material expandsgreater travel in are involved IJ03, IJ09, bend more on one side areduced print Care must be IJ17, IJ18, IJ19, actuator than on the other.head area taken that the IJ20, IJ21, IJ22, The expansion materials donot IJ23, IJ24, IJ27, may be thermal, delaminate IJ29, IJ30, IJ31,piezoelectric, Residual bend IJ32, IJ33, IJ34, magnetostrictive,resulting from IJ35, IJ36, IJ37, or other high temperature IJ38, IJ39,IJ42, mechanism. The or high stress IJ43, IJ44 bend actuator duringformation converts a high force low travel actuator mechanism to hightravel, lower force mechanism. Transient A trilayer bend Very good Highstresses IJ40, IJ41 bend actuator where the temperature are involvedactuator two outside layers stability Care must be are identical. ThisHigh speed, as taken that the cancels bend due a new drop can materialsdo not to ambient be fired before delaminate temperature and heatdissipates residual stress. The Cancels actuator only residual stress ofresponds to formation transient heating of one side or the other.Reverse The actuator loads Better Fabrication IJ05, IJ11 spring aspring. When the coupling to the complexity actuator is turned ink Highstress in off, the spring the spring releases. This can reverse theforce/distance curve of the actuator to make it compatible with theforce/time requirements of the drop ejection. Actuator A series of thinIncreased Increased Some stack actuators are travel fabricationpiezoelectric ink stacked. This can Reduced drive complexity jets beappropriate voltage Increased IJ04 where actuators possibility ofrequire high short circuits due electric field to pinholes strength,such as electrostatic and piezoelectric actuators. Multiple Multiplesmaller Increases the Actuator IJ12, IJ13, actuators actuators are usedforce available forces may not IJ18, IJ20, IJ22, simultaneously to froman actuator add linearly, IJ28, IJ42, IJ43 move the ink. Each Multiplereducing actuator need actuators can be efficiency provide only apositioned to portion of the control ink flow force required. accuratelyLinear A linear spring is Matches low Requires print IJ15 Spring used totransform a travel actuator head area for the motion with small withhigher spring travel and high travel force into a longer requirementstravel, lower force Non-contact motion. method of motion transformationCoiled A bend actuator is Increases Generally IJ17, IJ21, actuatorcoiled to provide travel restricted to IJ34, IJ35 greater travel in aReduces chip planar reduced chip area. area implementations Planar dueto extreme implementations fabrication are relatively difficulty in easyto fabricate. other orientations. Flexure A bend actuator Simple meansCare must be IJ10, IJ19, bend has a small region of increasing taken notto IJ33 actuator near the fixture travel of a bend exceed the point,which flexes actuator elastic limit in much more readily the flexurearea than the remainder Stress of the actuator. distribution is Theactuator very uneven flexing is Difficult to effectively accuratelymodel converted from an with finite even coiling to an element analysisangular bend, resulting in greater travel of the actuator tip. Catch Theactuator Very low Complex IJ10 controls a small actuator energyconstruction catch. The catch Very small Requires either enables oractuator size external force disables movement Unsuitable for of an inkpusher pigmented inks that is controlled in a bulk manner. Gears Gearscan be used Low force, Moving parts IJ13 to increase travel low travelare required at the expense of actuators can be Several duration.Circular used actuator cycles gears, rack and Can be are requiredpinion, ratchets, fabricated using More complex and other gearingstandard surface drive electronics methods can be MEMS Complex used.processes construction Friction, friction, and wear are possible BuckleA buckle plate can Very fast Must stay S. Hirata et al, plate be used tochange movement within elastic “An Ink-jet a slow actuator achievablelimits of the Head Using into a fast motion. materials for Diaphragm Itcan also convert long device life Microactuator”, a high force, low Highstresses Proc. IEEE travel actuator into involved MEMS, February a hightravel, Generally 1996, pp 418-423. medium force high power IJ18, IJ27motion. requirement Tapered A tapered Linearizes the Complex IJ14magnetic magnetic pole can magnetic construction pole increase travel atforce/distance the expense of curve force. Lever A lever and Matches lowHigh stress IJ32, IJ36, fulcrum is used to travel actuator around theIJ37 transform a motion with higher fulcrum with small travel travel andhigh force into requirements a motion with Fulcrum area longer traveland has no linear lower force. The movement, and lever can also can beused for a reverse the fluid seal direction of travel. Rotary Theactuator is High Complex IJ28 impeller connected to a mechanicalconstruction rotary impeller. A advantage Unsuitable for small angularThe ratio of pigmented inks deflection of the force to travel ofactuator results in the actuator can a rotation of the be matched toimpeller vanes, the nozzle which push the ink requirements by againststationary varying the vanes and out of number of the nozzle. impellervanes Acoustic A refractive or No moving Large area 1993 lensdiffractive (e.g. parts required Hadimioglu et zone plate) Only relevantal, EUP 550,192 acoustic lens is for acoustic ink 1993 Elrod et used toconcentrate jets al, EUP 572,220 sound waves. Sharp A sharp point isSimple Difficult to Tone-jet conductive used to concentrate constructionfabricate using point an electrostatic standard VLSI field. processesfor a surface ejecting ink-jet Only relevant for electrostatic ink jets

ACTUATOR MOTION Description Advantages Disadvantages Examples Volume Thevolume of the Simple High energy is Hewlett- expansion actuator changes,construction in typically Packard Thermal pushing the ink in the case ofrequired to Ink jet all directions. thermal ink jet achieve volume Canonexpansion. This Bubblejet leads to thermal stress, cavitation, andkogation in thermal ink jet implementations Linear, The actuatorEfficient High IJ01, IJ02, normal to moves in a coupling to inkfabrication IJ04, IJ07, IJ11, chip direction normal to drops ejectedcomplexity may IJ14 surface the print head normal to the be required tosurface. The surface achieve nozzle is typically perpendicular in theline of motion movement. Parallel to The actuator Suitable forFabrication IJ12, IJ13, chip moves parallel to planar complexity IJ15,IJ33,, IJ34, surface the print head fabrication Friction IJ35, IJ36surface. Drop Stiction ejection may still be normal to the surface.Membrane An actuator with a The effective Fabrication 1982 Howkins pushhigh force but area of the complexity U.S. Pat. No. 4,459,601 small areais used actuator Actuator size to push a stiff becomes the Difficulty ofmembrane that is membrane area integration in a in contact with the VLSIprocess ink. Rotary The actuator Rotary levers Device IJ05, IJ08, causesthe rotation may be used to complexity IJ13, IJ28 of some element,increase travel May have such a grill or Small chip friction at a pivotimpeller area point requirements Bend The actuator bends A very smallRequires the 1970 Kyser et when energized. change in actuator to be alU.S. Pat. No. This may be due to dimensions can made from at 3,946,398differential be converted to a least two distinct 1973 Stemme thermalexpansion, large motion. layers, or to have U.S. Pat. No. 3,747,120piezoelectric a thermal IJ03, IJ09, expansion, difference across IJ10,IJ19, IJ23, magnetostriction, the actuator IJ24, IJ25, IJ29, or otherform of IJ30, IJ31, IJ33, relative IJ34, IJ35 dimensional change. SwivelThe actuator Allows Inefficient IJ06 swivels around a operation wherecoupling to the central pivot. This the net linear ink motion motion issuitable force on the where there are paddle is zero opposite forcesSmall chip applied to opposite area sides of the paddle, requirementse.g. Lorenz force. Straighten The actuator is Can be used Requires IJ26,IJ32 normally bent, and with shape careful balance straightens whenmemory alloys of stresses to energized. where the ensure that theaustenic phase is quiescent bend is planar accurate Double The actuatorbends One actuator Difficult to IJ36, IJ37, bend in one direction can beused to make the drops IJ38 when one element power two ejected by bothis energized, and nozzles. bend directions bends the other Reduced chipidentical. way when another size. A small element is Not sensitiveefficiency loss energized. to ambient compared to temperature equivalentsingle bend actuators. Shear Energizing the Can increase Not readily1985 Fishbeck actuator causes a the effective applicable to U.S. Pat.No. 4,584,590 shear motion in the travel of other actuator actuatormaterial. piezoelectric mechanisms actuators Radial The actuatorRelatively High force 1970 Zoltan constriction squeezes an ink easy tofabricate required U.S. Pat. No. 3,683,212 reservoir, forcing singlenozzles Inefficient ink from a from glass Difficult to constrictednozzle. tubing as integrate with macroscopic VLSI processes structuresCoil/ A coiled actuator Easy to Difficult to IJ17, IJ21, uncoil uncoilsor coils fabricate as a fabricate for IJ34, IJ35 more tightly. Theplanar VLSI non-planar motion of the free process devices end of theactuator Small area Poor out-of- ejects the ink. required, planestiffness therefore low cost Bow The actuator bows Can increase MaximumIJ16, IJ18, (or buckles) in the the speed of travel is IJ27 middle whentravel constrained energized. Mechanically High force rigid requiredPush-Pull Two actuators The structure Not readily IJ18 control ashutter. is pinned at both suitable for ink One actuator pulls ends, sohas a jets which the shutter, and the high out-of- directly push theother pushes it. plane rigidity ink Curl A set of actuators Good fluidDesign IJ20, IJ42 inwards curl inwards to flow to the complexity reducethe volume region behind of ink that they the actuator enclose.increases efficiency Curl A set of actuators Relatively Relatively IJ43outwards curl outwards, simple large chip area pressurizing ink inconstruction a chamber surrounding the actuators, and expelling ink froma nozzle in the chamber. Iris Multiple vanes High High IJ22 enclose avolume efficiency fabrication of ink. These Small chip complexitysimultaneously area Not suitable rotate, reducing for pigmented thevolume inks between the vanes. Acoustic The actuator The actuator Largearea 1993 vibration vibrates at a high can be required for Hadimioglu etfrequency. physically efficient al, EUP 550,192 distant from theoperation at 1993 Elrod et ink useful al, EUP 572,220 frequenciesAcoustic coupling and crosstalk Complex drive circuitry Poor control ofdrop volume and position None In various ink jet No moving Various otherSilverbrook, designs the parts tradeoffs are EP 0771 658 A2 actuatordoes not required to and related move. eliminate patent moving partsapplications Tone-jet

NOZZLE REFILL METHOD Description Advantages Disadvantages ExamplesSurface This is the normal Fabrication Low speed Thermal ink tension waythat ink jets simplicity Surface jet are refilled. After Operationaltension force Piezoelectric the actuator is simplicity relatively smallink jet energized, it compared to IJ01-IJ07, typically returns actuatorforce IJ10-IJ14, IJ16, rapidly to its Long refill IJ20, IJ22-IJ45 normalposition. time usually This rapid return dominates the sucks in airtotal repetition through the nozzle rate opening. The ink surfacetension at the nozzle then exerts a small force restoring the meniscusto a minimum area. This force refills the nozzle. Shuttered Ink to thenozzle High speed Requires IJ08, IJ13, oscillating chamber is Lowactuator common ink IJ15, IJ17, IJ18, ink provided at a energy, as thepressure IJ19, IJ21 pressure pressure that actuator need oscillatoroscillates at twice only open or May not be the drop ejection close theshutter, suitable for frequency. When a instead of pigmented inks dropis to be ejecting the ink ejected, the shutter drop is opened for 3 halfcycles: drop ejection, actuator return, and refill. The shutter is thenclosed to prevent the nozzle chamber emptying during the next negativepressure cycle. Refill After the main High speed, as Requires two IJ09actuator actuator has the nozzle is independent ejected a drop aactively refilled actuators per second (refill) nozzle actuator isenergized. The refill actuator pushes ink into the nozzle chamber. Therefill actuator returns slowly, to prevent its return from emptying thechamber again. Positive The ink is held a High refill Surface spillSilverbrook, ink slight positive rate, therefore a must be EP 0771 658A2 pressure pressure. After the high drop prevented and related ink dropis ejected, repetition rate is Highly patent the nozzle possiblehydrophobic applications chamber fills print head Alternative quickly assurface surfaces are for:, IJ01-IJ07, tension and ink requiredIJ10-IJ14, IJ16, pressure both IJ20, IJ22-IJ45 operate to refill thenozzle.

METHOD OF RESTRICTING BACK-FLOW THROUGH INLET Description AdvantagesDisadvantages Examples Long inlet The ink inlet Design Restricts refillThermal ink channel channel to the simplicity rate jet nozzle chamber isOperational May result in Piezoelectric made long and simplicity arelatively large ink jet relatively narrow, Reduces chip area IJ42, IJ43relying on viscous crosstalk Only partially drag to reduce effectiveinlet back-flow. Positive The ink is under a Drop selection Requires aSilverbrook, ink positive pressure, and separation method (such as EP0771 658 A2 pressure so that in the forces can be a nozzle rim or andrelated quiescent state reduced effective patent some of the ink Fastrefill time hydrophobizing, applications drop already or both) toPossible protrudes from the prevent flooding operation of the nozzle. ofthe ejection following: IJ01-IJ07, This reduces the surface of theIJ09-IJ12, pressure in the print head. IJ14, IJ16, IJ20, nozzle chamberIJ22,, IJ23-IJ34, which is required IJ36-IJ41, IJ44 to eject a certainvolume of ink. The reduction in chamber pressure results in a reductionin ink pushed out through the inlet. Baffle One or more The refill rateDesign HP Thermal baffles are placed is not as complexity Ink Jet in theinlet ink restricted as the May increase Tektronix flow. When the longinlet fabrication piezoelectric ink actuator is method. complexity (e.g.jet energized, the Reduces Tektronix hot rapid ink crosstalk meltmovement creates Piezoelectric eddies which print heads). restrict theflow through the inlet. The slower refill process is unrestricted, anddoes not result in eddies. Flexible In this method Significantly Notapplicable Canon flap recently disclosed reduces back- to most ink jetrestricts by Canon, the flow for edge- configurations inlet expandingactuator shooter thermal Increased (bubble) pushes on ink jet devicesfabrication a flexible flap that complexity restricts the inlet.Inelastic deformation of polymer flap results in creep over extended useInlet filter A filter is located Additional Restricts refill IJ04, IJ12,between the ink advantage of ink rate IJ24, IJ27, IJ29, inlet and thefiltration May result in IJ30 nozzle chamber. Ink filter may complex Thefilter has a be fabricated construction multitude of small with no holesor slots, additional restricting ink process steps flow. The filter alsoremoves particles which may block the nozzle. Small The ink inlet DesignRestricts refill IJ02, IJ37, inlet channel to the simplicity rate IJ44compared nozzle chamber May result in to nozzle has a substantially arelatively large smaller cross chip area section than that of Onlypartially the nozzle, effective resulting in easier ink egress out ofthe nozzle than out of the inlet. Inlet A secondary Increases RequiresIJ09 shutter actuator controls speed of the ink- separate refill theposition of a jet print head actuator and shutter, closing off operationdrive circuit the ink inlet when the main actuator is energized. Theinlet The method avoids Back-flow Requires IJ01, IJ03, is located theproblem of problem is careful design to IJ05, IJ06, IJ07, behind inletback-flow by eliminated minimize the IJ10, IJ11, IJ14, the ink-arranging the ink- negative IJ16, IJ22, IJ23, pushing pushing surface ofpressure behind IJ25, IJ28, IJ31, surface the actuator the paddle IJ32,IJ33, IJ34, between the inlet IJ35, IJ36, IJ39, and the nozzle. IJ40,IJ41 Part of The actuator and a Significant Small increase IJ07, IJ20,the wall of the ink reductions in in fabrication IJ26, IJ38 actuatorchamber are back-flow can be complexity moves to arranged so thatachieved shut off the motion of the Compact the inlet actuator closesoff designs possible the inlet. Nozzle In some Ink back-flow Nonerelated Silverbrook, actuator configurations of problem is to inkback-flow EP 0771 658 A2 does not ink jet, there is no eliminated onactuation and related result in expansion or patent ink back- movementof an applications flow actuator which Valve-jet may cause ink Tone-jetback-flow through the inlet.

NOZZLE CLEARING METHOD Description Advantages Disadvantages ExamplesNormal All of the nozzles No added May not be Most ink jet nozzle arefired complexity on sufficient to systems firing periodically, the printhead displace dried IJ01, IJ02, before the ink has ink IJ03, IJ04, IJ05,a chance to dry. IJ06, IJ07, IJ09, When not in use IJ10, IJ11, IJ12, thenozzles are IJ14, IJ16, IJ20, sealed (capped) IJ22, IJ23, IJ24, againstair. IJ25, IJ26, IJ27, The nozzle firing IJ28, IJ29, IJ30, is usuallyIJ31, IJ32, IJ33, performed during a IJ34, IJ36, IJ37, special clearingIJ38, IJ39, IJ40,, cycle, after first IJ41, IJ42, IJ43, moving the printIJ44,, IJ45 head to a cleaning station. Extra In systems which Can behighly Requires Silverbrook, power to heat the ink, but do effective ifthe higher drive EP 0771 658 A2 ink heater not boil it under heater isvoltage for and related normal situations, adjacent to the clearingpatent nozzle clearing can nozzle May require applications be achievedby larger drive over-powering the transistors heater and boiling ink atthe nozzle. Rapid The actuator is Does not Effectiveness May be usedsuccession fired in rapid require extra depends with: IJ01, IJ02, ofsuccession. In drive circuits on substantially IJ03, IJ04, IJ05,actuator some the print head upon the IJ06, IJ07, IJ09, pulsesconfigurations, this Can be readily configuration of IJ10, IJ11, IJ14,may cause heat controlled and the ink jet nozzle IJ16, IJ20, IJ22,build-up at the initiated by IJ23, IJ24, IJ25, nozzle which boilsdigital logic IJ27, IJ28, IJ29, the ink, clearing IJ30, IJ31, IJ32, thenozzle. In other IJ33, IJ34, IJ36, situations, it may IJ37, IJ38, IJ39,cause sufficient IJ40, IJ41, IJ42, vibrations to IJ43, IJ44, IJ45dislodge clogged nozzles. Extra Where an actuator A simple Not suitableMay be used power to is not normally solution where where there is awith: IJ03, IJ09, ink driven to the limit applicable hard limit to IJ16,IJ20, IJ23, pushing of its motion, actuator IJ24, IJ25, IJ27, actuatornozzle clearing movement IJ29, IJ30, IJ31, may be assisted by IJ32,IJ39, IJ40, providing an IJ41, IJ42, IJ43, enhanced drive IJ44, IJ45signal to the actuator. Acoustic An ultrasonic A high nozzle High IJ08,IJ13, resonance wave is applied to clearing implementation IJ15, IJ17,IJ18, the ink chamber. capability can be cost if system IJ19, IJ21 Thiswave is of an achieved does not already appropriate May be include anamplitude and implemented at acoustic actuator frequency to cause verylow cost in sufficient force at systems which the nozzle to clearalready include blockages. This is acoustic easiest to achieve actuatorsif the ultrasonic wave is at a resonant frequency of the ink cavity.Nozzle A microfabricated Can clear Accurate Silverbrook, clearing plateis pushed severely clogged mechanical EP 0771 658 A2 plate against thenozzles alignment is and related nozzles. The plate required patent hasa post for Moving parts applications every nozzle. A are required postmoves There is risk through each of damage to the nozzle, displacingnozzles dried ink. Accurate fabrication is required Ink The pressure ofthe May be Requires May be used pressure ink is temporarily effectivewhere pressure pump with all IJ series pulse increased so that othermethods or other pressure ink jets ink streams from cannot be usedactuator all of the nozzles. Expensive This may be used Wasteful of inconjunction ink with actuator energizing. Print A flexible ‘blade’Effective for Difficult to Many ink jet head is wiped across the planarprint head use if print head systems wiper print head surface. surfacessurface is non- The blade is Low cost planar or very usually fabricatedfragile from a flexible Requires polymer, e.g. mechanical parts rubberor synthetic Blade can elastomer. wear out in high volume print systemsSeparate A separate heater Can be Fabrication Can be used ink isprovided at the effective where complexity with many IJ boiling nozzlealthough other nozzle series ink jets heater the normal drop e- clearingmethods ection mechanism cannot be used does not require it. Can be Theheaters do not implemented at require individual no additional drivecircuits, as cost in some ink many nozzles can jet be clearedconfigurations simultaneously, and no imaging is required.

NOZZLE PLATE CONSTRUCTION Description Advantages Disadvantages ExamplesElectro- A nozzle plate is Fabrication High Hewlett formed separatelysimplicity temperatures and Packard Thermal nickel fabricated frompressures are Ink jet electroformed required to bond nickel, and bondednozzle plate to the print head Minimum chip. thickness constraintsDifferential thermal expansion Laser Individual nozzle No masks Eachhole Canon ablated or holes are ablated required must be Bubblejetdrilled by an intense UV Can be quite individually 1988 Sercel etpolymer laser in a nozzle fast formed al., SPIE, Vol. plate, which isSome control Special 998 Excimer typically a over nozzle equipment Beampolymer such as profile is required Applications, pp. polyimide orpossible Slow where 76-83 polysulphone Equipment there are many 1993required is thousands of Watanabe et al., relatively low nozzles perprint U.S. Pat. No. 5,208,604 cost head May produce thin burrs at exitholes Silicon A separate nozzle High accuracy Two part K. Bean, micro-plate is is attainable construction IEEE machined micromachined Highcost Transactions on from single crystal Requires Electron silicon, andprecision Devices, Vol. bonded to the print alignment ED-25, No. 10,head wafer. Nozzles may 1978, pp 1185-1195 be clogged by Xerox 1990adhesive Hawkins et al., U.S. Pat. No. 4,899,181 Glass Fine glass Noexpensive Very small 1970 Zoltan capillaries capillaries are equipmentnozzle sizes are U.S. Pat. No. 3,683,212 drawn from glass requireddifficult to form tubing. This Simple to Not suited for method has beenmake single mass production used for making nozzles individual nozzles,but is difficult to use for bulk manufacturing of print heads withthousands of nozzles. Monolithic, The nozzle plate is High accuracyRequires Silverbrook, surface deposited as a (<1 μm) sacrificial layerEP 0771 658 A2 micro- layer using Monolithic under the nozzle andrelated machined standard VLSI Low cost plate to form the patent usingdeposition Existing nozzle chamber applications VLSI techniques.processes can be Surface may IJ01, IJ02, litho- Nozzles are etched usedbe fragile to the IJ04, IJ11, IJ12, graphic in the nozzle plate touchIJ17, IJ18, IJ20, processes using VLSI IJ22, IJ24, IJ27, lithography andIJ28, IJ29, IJ30, etching. IJ31, IJ32, IJ33, IJ34, IJ36, IJ37, IJ38,IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Monolithic, The nozzle plate is Highaccuracy Requires long IJ03, IJ05, etched a buried etch stop (<1 μm)etch times IJ06, IJ07, IJ08, through in the wafer. Monolithic Requires aIJ09, IJ10, IJ13, substrate Nozzle chambers Low cost support wafer IJ14,IJ15, IJ16, are etched in the No differential IJ19, IJ21, IJ23, front ofthe wafer, expansion IJ25, IJ26 and the wafer is thinned from the backside. Nozzles are then etched in the etch stop layer. No nozzle Variousmethods No nozzles to Difficult to Ricoh 1995 plate have been tried tobecome clogged control drop Sekiya et al U.S. Pat. No. eliminate theposition 5,412,413 nozzles entirely, to accurately 1993 prevent nozzleCrosstalk Hadimioglu et al clogging. These problems EUP 550,192 includethermal 1993 Elrod et bubble al EUP 572,220 mechanisms and acoustic lensmechanisms Trough Each drop ejector Reduced Drop firing IJ35 has atrough manufacturing direction is through which a complexity sensitiveto paddle moves. Monolithic wicking. There is no nozzle plate. Nozzleslit The elimination of No nozzles to Difficult to 1989 Saito et insteadof nozzle holes and become clogged control drop al U.S. Pat. No.individual replacement by a position 4,799,068 nozzles slit encompassingaccurately many actuator Crosstalk positions reduces problems nozzleclogging, but increases crosstalk due to ink surface waves

DROP EJECTION DIRECTION Description Advantages Disadvantages ExamplesEdge Ink flow is along Simple Nozzles Canon (‘edge the surface of theconstruction limited to edge Bubblejet 1979 shooter’) chip, and inkdrops No silicon High Endo et al GB are ejected from etching requiredresolution is patent 2,007,162 the chip edge. Good heat difficult Xeroxheater- sinking via Fast color in-pit 1990 substrate printing requiresHawkins et al Mechanically one print head U.S. Pat. No. 4,899,181 strongper color Tone-jet Ease of chip handing Surface Ink flow is along Nobulk Maximum ink Hewlett- (‘roof the surface of the silicon etching flowis severely Packard TIJ shooter’) chip, and ink drops requiredrestricted 1982 Vaught et are ejected from Silicon can al U.S. Pat. No.the chip surface, make an 4,490,728 normal to the effective heat IJ02,IJ11, plane of the chip. sink IJ12, IJ20, IJ22 Mechanical strengthThrough Ink flow is through High ink flow Requires bulk Silverbrook,chip, the chip, and ink Suitable for silicon etching EP 0771 658 A2forward drops are ejected pagewidth print and related (‘up from thefront heads patent shooter’) surface of the chip. High nozzleapplications packing density IJ04, IJ17, therefore low IJ18, IJ24,IJ27-IJ45 manufacturing cost Through Ink flow is through High ink flowRequires IJ01, IJ03, chip, the chip, and ink Suitable for wafer thinningIJ05, IJ06, IJ07, reverse drops are ejected pagewidth print RequiresIJ08, IJ09, IJ10, (‘down from the rear heads special handling IJ13,IJ14, IJ15, shooter’) surface of the chip. High nozzle during IJ16,IJ19, IJ21, packing density manufacture IJ23, IJ25, IJ26 therefore lowmanufacturing cost Through Ink flow is through Suitable for PagewidthEpson Stylus actuator the actuator, which piezoelectric print headsTektronix hot is not fabricated as print heads require several melt partof the same thousand piezoelectric ink substrate as the connections tojets drive transistors. drive circuits Cannot be manufactured instandard CMOS fabs Complex assembly required

INK TYPE Description Advantages Disadvantages Examples Aqueous, Waterbased ink Environmentally Slow drying Most existing dye which typicallyfriendly Corrosive ink jets contains: water, No odor Bleeds on All IJseries dye, surfactant, paper ink jets humectant, and May Silverbrook,biocide. strikethrough EP 0771 658 A2 Modern ink dyes Cockles paper andrelated have high water- patent fastness, light applications fastnessAqueous, Water based ink Environmentally Slow drying IJ02, IJ04, pigmentwhich typically friendly Corrosive IJ21, IJ26, IJ27, contains: water, Noodor Pigment may IJ30 pigment, Reduced bleed clog nozzles Silverbrook,surfactant, Reduced Pigment may EP 0771 658 A2 humectant, and wickingclog actuator and related biocide. Reduced mechanisms patent Pigmentshave an strikethrough Cockles paper applications advantage inPiezoelectric reduced bleed, ink-jets wicking and Thermal inkstrikethrough. jets (with significant restrictions) Methyl MEK is ahighly Very fast Odorous All IJ series Ethyl volatile solvent dryingFlammable ink jets Ketone used for industrial Prints on (MEK) printingon various difficult surfaces substrates such such as as metals andluminium cans. plastics Alcohol Alcohol based inks Fast drying Slightodor All IJ series (ethanol, can be used where Operates at Flammable inkjets 2-butanol, the printer must sub-freezing and operate attemperatures others) temperatures Reduced below the freezing papercockle point of water. An Low cost example of this is in-camera consumerphotographic printing. Phase The ink is solid at No drying Highviscosity Tektronix hot change room temperature, time-ink Printed inkmelt (hot melt) and is melted in instantly freezes typically has apiezoelectric ink the print head on the print ‘waxy’ feel jets beforejetting. Hot medium Printed pages 1989 Nowak melt inks are Almost anymay ‘block’ U.S. Pat. No. 4,820,346 usually wax based, print medium InkAll IJ series with a melting can be used temperature may ink jets pointaround 80° C. No paper be above the After jetting cockle occurs curiepoint of the ink freezes No wicking permanent almost instantly occursmagnets upon contacting No bleed Ink heaters the print medium occursconsume power or a transfer roller. No Long warm- strikethrough up timeoccurs Oil Oil based inks are High High All IJ series extensively usedin solubility viscosity: this is ink jets offset printing. medium for asignificant They have some dyes limitation for use advantages in Doesnot in ink jets, which improved cockle paper usually require acharacteristics on Does not wick low viscosity. paper (especiallythrough paper Some short no wicking or chain and multi- cockle). Oilbranched oils soluble dies and have a pigments are sufficiently lowrequired. viscosity. Slow drying Micro- A microemulsion Stops inkViscosity All IJ series emulsion is a stable, self bleed higher than inkjets forming emulsion High dye water of oil, water, and solubility Costis surfactant. The Water, oil, slightly higher characteristic drop andamphiphilic than water based size is less than soluble dies can ink 100nm, and is be used High determined by the Can stabilize surfactantpreferred curvature pigment concentration of the surfactant. suspensionsrequired (around 5%)

1. An inkjet printhead comprising: a plurality of nozzles; a bubbleforming chamber corresponding to each of the nozzles respectively, thebubble forming chambers adapted to contain a bubble forming liquid; aheater element disposed in each of the bubble forming chambersrespectively, the heater elements configured for thermal contact withthe bubble forming liquid; and, a pair of electrodes for each of theheater elements respectively, the pair of electrodes in each of thebubble forming chambers being positioned adjacent each other such thatthe heater element provides a single current path between the electrodesof each pair; wherein, each of the heater elements has a double omegashape in which a smaller, inner omega shape is concentric with, andencircled by, a larger, outer omega shape.
 2. The inkjet printheadaccording to claim 1, wherein the bubble forming chamber has a circularcross section, the circular cross section being concentric with theinner and outer omega shapes forming the double omega shaped heaterelement.
 3. The inkjet printhead according to claim 1, wherein eachbubble forming chamber is cylindrical.
 4. The inkjet printhead accordingto claim 1, further comprising: an underlying substrate; a unitaryamorphous ceramic structure having a nozzle plate with a plurality ofnozzles formed therein; and an array of sidewalls extending from oneside of the nozzle plate to the underlying substrate, wherein theunderlying substrate, the nozzle plate and the array of sidewalls definethe bubble forming chambers.
 5. The inkjet printhead according to claim1, wherein the printhead is a pagewidth printhead.
 6. The inkjetprinthead according to claim 1, wherein the heater elements are actuatedby one or more drive circuits which are located partially on a side ofone of the bubble forming chambers.
 7. The ink jet printhead accordingto claim 6, wherein the one or more drive circuits conduct a thermalpulse in order to form a gas bubble in the bubble forming liquid.
 8. Theinkjet printhead according to claim 1, wherein the bubble formingchamber is in fluid communication with an inlet passage, the inletpassage and the nozzle both having a circular cross section and bothbeing concentric with the double omega shaped heater element.